google protobuf: do not generate discovery
google protobuf: do not generate discovery

R=vadimsh@chromium.org
BUG=
NOTRY=true
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1834253003

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go